The invention relates to a rectifier diode including a press-fit base provided with an axially extending securing region for a semiconductor chip, a head wire secured to the semiconductor chip and an encapsulation of the head wire as well as means for tension relief of the head wire.
It is known to make rectifier diodes for medium and high capacity in the form of press-fit diodes. The press-fit diodes have a press-fit base that is press-fitted into a corresponding recess of a securing element. At the same time, the securing element takes on the task of permanent thermal and electrical connection of the rectifier diode. Such arrangements are known in automotive engineering, for instance, where they are used as rectifiers in motor vehicle generators. The press-fit base has a securing region on which a semiconductor chip is secured, for instance by soldering. Secured on the semiconductor chip in turn, likewise by soldering, for instance, is a so-called head wire, which is firmly connected electrically, for instance by soldering or welding, to a phase supply line of the motor vehicle generator.
In motor vehicle operation, vibration occurs, which is transmitted via the vehicle generator to the rectifier diode and expose it to considerable tensile strain. To enable reducing this tensile strain, it is known to encapsulate the rectifier diode and thus to establish a positive engagement between the head wire and the press-fit base. This positive engagement is intended to provide relief of tensile strain for the vulnerable semiconductor chip and the solder layers between the semiconductor chip and the press-fit base, on the one hand, and the head wire, on the other.
To enable increasing this tension relief, it has already been proposed, such as in German Published, Non-Examined Patent Application DE-OS 41 12 286, that additional means be provided that protrude into the encapsulation. DE 41 12 286 describes a wall extending obliquely beside the semiconductor chip and enclosed by the encapsulation. The wall is located in the immediate vicinity of the semiconductor chip and has a height that protrudes above the semiconductor chip. In this embodiment, the desired tension relief can be controlled solely by way of the height of the wall. It is disadvantageous, however, that the higher the wall, the more the semiconductor chip is shielded before the encapsulation is made, so that the side faces of the chip, after the semiconductor chip has been soldered in place, are only very poorly accessible for passivation.
It is an object of the present invention to provide an improved rectifier diode of the above-described type which does not have the above-described disadvantages.
According to the invention, the rectifier diode comprises a press-fit base including an axially extending securing region for the semiconductor chip; a head wire attached to the semiconductor chip; an encapsulation for at least a portion of the axially extending securing region and an end portion of the head wire connected to the semiconductor chip and a collar arranged extending from a peripheral end portion of the securing region, extending axially beyond a securing face for the semiconductor chip on the securing region and inclined to an axis of the securing region. The securing face is closer to the head wire than an outer edge region of the press-fit base, the collar is in one-piece with the securing region, the collar includes a first portion and a second portion, the first portion extends from the peripheral end portion of the securing region and is inclined to the axis at a first positive angle and the second portion of the collar extends from the first portion and is inclined at a second positive angle such that the second positive angle is greater than the first positive angle.
The rectifier diode according to the invention has the advantage over the prior art that a reliable tension relief of the rectifier diode is attained in a simple way, and access by a passivation agent to the side faces of the semiconductor chip is not made more difficult. Because a collar extending at an angle to an axial of the securing region and preferably protruding axially beyond a securing face of the securing region is located on an outer encompassing termination of the securing region, it is possible by simple geometrical variations of the collar to exert an influence on the encapsulation parameters that substantially affect the tension relief. Particularly by an advantageous selection of the length and/or approach angle and/or the shaping of the collar, a length of the encapsulation that is decisive for the tension relief can be established as a function of other known parameters, such as the modulus of elasticity of the encapsulation.
In a preferred feature of the invention, the collar is formed of individual spaced-apart segments, so that there is always a gap between each collar segment. As a result of this feature it is highly advantageously possible not only, as already noted, to increase the tension relief substantially, but also to assure unhindered flow of a passivation agent to the semiconductor chip.